DESCRIPTION (adapted from the application) Osteoporosis affects 25-30 million American adults, primarily post-menopausal women. The development of osteoporosis and fractures in later life depends not only on the rate of bone loss, but also on peak bone mass, most of which is acquired during adolescence and early adulthood. Anorexia nervosa is a disease of adolescence that affects 1 in 200 adolescent females and is associated with profound osteopenia and increased fracture risk. The degree of osteopenia depends on the age of onset and duration of amenorrhea and the bone loss may not be reversible. In post-menopausal women, oral alendronate increases bone mass in the spine, hip and total body and reduces the risk of fractures. The efficacy of this treatment has not been evaluated in anorexia nervosa. The objective of this pilot study is to test the hypothesis that oral alendronate increases bone mass in adolescents with anorexia nervosa. The adolescent age group was chosen because adolescence is the critical time period during which 40-60% of peak bone mass is accrued. Eligible subjects with anorexia nervosa, aged 13-21 years, will be randomized to receive either oral alendronate or placebo. Whole body, vertebral spine and femoral neck bone mineral density will be measured by dual energy absorptiometry (DEXA) at baseline, and after one year of treatment. Serum and urine markers of bone turnover will be measured at baseline and after 6 and 12 months of treatment. Changes in bone mineral density and markers of bone turnover will be compared between groups and will be correlated with nutritional intake, body weight, hormonal status and measures of body composition. The results of this pilot study will aid in the planning of a larger multi-center double-blind randomized placebo-controlled trial evaluating the safety and efficacy of alendronate in the treatment of osteopenia in adolescents with anorexia nervosa.